Ch 5. Principles of Inheritance and Variations (Stack 1) Flashcards
Define Genetics
Genetics is the branch of science which deals with the study of inheritance, as well as the variation of characters from parent to offspring.
Define inheritance. (K) / Define heredity
Inheritance is the process by which characters are passed on from parent to progeny.
Define variation
Variation is the degree by which offspring differ from their parents
Define a gene.
Gene is the unit of inheritance which contains the information that is required to express a particular trait in an organism.
Define alleles.
Genes which codes for a pair of contrasting traits are known as alleles. they are slightly different fonns of same gene
or
Alternate forms of a gene are called Alleles.
What is a dominant allele?
It is one of pair of genes which can express itself whether present in homozygous or heterozygous state.
What is a recessive allele?
The allele which is unable to express in the presence of its contrasting factor in a heterozygous condition is called recessive allele.
What is genotype?
It is the genetic constitution of an individual with regard to one or more characters irrespective of whether the genes are expressed or not.
What is phenotype?
It is the observable or measurable distinctive structural or functional characteristic of an individual with regard to one or more characters.
What are homozygous individuals?
Individuals which have the identical alleles of a gene or factors of a character on homologous chromosome
What are heterozygous individuals?
Individuals which have the two contrasting factors of a character or two different alleles of a gene on homologous chromosome.
What is a true breeding plant?
A true breeding plant is one that, when self-fertilised, only produces offspring with the same trait.
True breeding organisms are genetically identical and have identical alleles for a trait.
What is monohybrid cross?
It is a cross between two organisms of a species which is made to study the inheritance of a single pair of alleles or factors of a character.
What is Punnette square?
Punnette square is a graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross.
Mention the phenotypic ratio of monohybrid cross.
3:I
Mention the genotypic ratio of monohybrid cross
l :2:1
What is a test cross?
The crossing of an organism with a homozygous recessive parent in order to determine whether it is homozygous or heterozygous for a particular character is called a test cross.
Mention monohybrid test cross ratio
1:1
Mention the significance of test cross
The purpose of a test cross is to determine if this individual is homozygous dominant or heterozygous
State the law of segregation.
Law of segregation states that “Though the parents contain two alleles during gamete formation, the factors or alleles of a pair segregate from each other such that a gamete receives only one of the two factors”
Mention the botanical name of the plant used by Mendel
Pisum sativum
How many traits were studied by Mendel
Seven pairs
Name the technique used by Mendel to prevent self pollination in pea flowers
Emasculation
Differentiate between homozygous and heterozygous conditions.
Homozygous
- Both the alleles of a character are similar.
- It produces only one type of gamete.
- It gives rise to similar homozygous individuals.
Heterozygous
- It carries dissimilar alleles.
- It produces two types of gametes.
- It gives rise to different types of genotypes.
Differentiate dominant and recessive alleles
Dominant Alleles
(i) It is able to express itself even in the presence of its recessive allele.
(ii) Its effect can be seen in both heterozygous and homozygous condition
Recessive Alleles
(i) Recessive allele or factor is unable to express its effect in the presence of dominant.
(i) Its effect can be seen only in homozygous condition.
Define incomplete dominance
Incomplete dominance is the phenomenon where none of the two alleles of a gene is dominant over each other so that when both of them are present together, a new phenotype is formed which is somewhat intermediate between the independent expression of two alleles.
Mention the phenotypic ratio and genotype ratio with respect to incomplete dominance in Snapdragon
1: 2:1
(RR) Red: (Rr) Pink: (rr) White
What is incomplete dominance?
Mention an example
Incomplete dominance is the phenomenon where none of the two alleles of a gene is dominant over each other so that when both of them are present together, a new phenotype is formed which is somewhat intermediate between the independent expression of two alleles.
Example: Inheritance of flower colour in Antirrhinum or snapdragon.
Define codominance
When two alleles for a trait are equally expressed with neither being recessive or dominant, is called codominance.
What are multiple alleles?
When there are more than two, alleles, governing the same character is called multiple alleles .
Mention an example for multiple allelism
Inheritance of ABO blood groups system is an example
How many genotypes are possible for the four blood groups in ABO blood group system?
Six genotypes are possible
A child has blood group ‘O’. If the father has blood group ‘ A’ and mother blood group ·B’, work out the genotypes of the parents and the possible genotypes of the other offspring.
A child with ‘ O’ blood must have the homozygous recessive condition for the character.
Paternal contribution and maternal contribution of a recessive allele each. Hence, the father must have I^Ai and mother must have l^Bi alleles.
